It's good to replace it if it's still the original t-stat. But, it may not fix your problem because it appears your t-stat is working. During stop and go driving the temp rises because the coolant circulation is slow and air flow is weak. The opposite happens during straight driving. The coolant circulates faster and the air flow is better. So, based on your temp change of 100* to 45* the t-stat is allowing the coolant to flow.... will a new thermostat fix the problem??
It did for me but I had a china made T-stat and It would not open all the way. BIG DIFFERENCE!I have a 2993 300d turbo diesel and in town (stop and go) it runs hot. (above 100C) and on the highway doing 45+ the temperature is great. will a new thermostat fix the problem??
GERMAN STAR has the best price for Sachs made in Germany verified...I got one for @$130.00 and I recommend them (FAST SHIPPING!)And make sure the fan clutch gets replaced too with a Behr (Made in Germany) or a Fichtel&Sachs.
Bad fan clutches are the #1 contributor to hot running engine temps apart from a bad thermostat.